I have used many SD cards in the decade I have had my PMD620. Speeds ranging from class 4 to class 10, mostly SanDisk, but also a few Lexar, Sony and Transcend, and never had an issue. I think it's just not very picky about cards (at least genuine ones from decent manufacturers).

Be somewhat careful about where you buy these brand-name items, since there is some counterfeiting in the picture. I wonder whether someone's allegation that a certain brand had "had problems lately" might be because the cards with the actual problems weren't from the manufacturer whose name was on the product.

Also, don't assume that a recorder's highest sampling rate is automatically the best choice in all circumstances.